Ophthalmologists use a variety of devices for imaging of a patient's eye, including slit-lamps, ophthalmoscopes, fundus cameras, and scanning laser ophthalmoscopes (SLOs). The ophthalmic slit-lamp examination has remained largely unchanged for over sixty years. The slit lamp is a versatile instrument used by ophthalmologists for examining a patient's eye. It consists of a microscope, an illumination source, and a mechanical support system to facilitate positioning the illumination source at various angles with respect to the eye. Ophthalmologists and optometrists typically examine the eye by first horizontally scanning across the eye using various slit beam thicknesses and orientations to examine the most anterior structures such as the cornea and conjunctiva. Then the examiner will adjust the focus plane posterior to horizontally scan across the anterior chamber of the eye. The focus is then adjusted more posteriorly to horizontally scan across the iris and anterior crystalline lens. The process is repeated again to examine the posterior aspect of the crystalline lens and anterior vitreous.
FIG. 1 shows a schematic view of a patient's eye. As shown in FIG. 1, the basic components of the eye 10 include a cornea 12, conjunctiva 14, an iris 16, a pupil 18, a crystalline lens 20, and a retina 22. An anterior chamber 24 is provided behind the cornea 12. A posterior chamber 40 is provided posterior of anterior chamber 24. The posterior chamber 40 includes the lens 20 which is positioned by the suspensory ligaments 34 of the eye. An anterior capsule 31 separates the anterior chamber 24 from a posterior chamber 40 and a posterior capsule 30 separates the posterior chamber 40 from a chamber 32 which includes the vitreous humor. Light enters the front of the eye through the pupil 18, is focused and inverted by the cornea and lens 20, and is projected onto the retina 22 at the back of the eye. The iris 16 functions as an “aperture” that opens and closes to regulate the amount of light entering the eye. The cornea, iris, pupil and lens are often referred to as the anterior segment of the eye. The retina 22 is a multi-layered structure that converts received light into a neural signal through a process known as “signal transduction.” The photoreceptors on the retina are known as rods and cones. These generate neural signals that are communicated to the brain by ganglion cells that form the optic nerve 24.
Anterior segment ocular imaging (e.g., slit-lamp) photography allows ophthalmologists to document and record a given slit-lamp view of an eye. Similarly, slit-lamp video allows ophthalmologists to document and record a slit-lamp examination of a patient's eye. Traditional slit-lamp photography creates an image using a sensor placed in an optical system at a plane optically conjugate to an object which is to be imaged. This is the plane at which the best focus is achieved and therefore the best optical resolution of features in the object results.
Most still and video photography slit-lamp units are created by mounting a camera in place of the viewing oculars or in conjunction with the viewing oculars through the means of a beam splitter. These traditional modalities of recording the slit-lamp exam are limited to either using still photography to capture a single moment of the examination, or taking a video of one's own examination sequence of slit-beam focus, magnification, slit-beam height, width and angle of incidence. Another health care professional can view the video, but cannot alter any of these variables after the examination. Slit-lamp video also requires a highly trained ophthalmologist or optometrist to perform the examination. No system exists that allows an ophthalmologist or optometrist to perform a virtual slit-lamp examination based on images obtained at an earlier time. Such a system using traditional cameras would require a massive library of images of various slit-beam positions and characteristics would be required, with numerous sequential images stored in at least the x- and z-axes.
A camera captures an image of the illuminated portion of the eye structures via reflected light. Rays which emanate from a point within the object plane in multiple directions are captured by the optical system and those rays converge to approximately a single point in the conjugate image plane. The set of rays which are summed at any image point is generally constrained by physical apertures placed within the optical assembly. The traditional sensor records the summation of the intensity of light in the plane of the detector. The measurement contains the intensity distribution of light within the plane of the sensor but loses all information about the rays' direction before the summation. Therefore the typical process of recording a traditional image does not record a very large fraction of the information contained in the light absorbed.